1. Field of the Invention
The present invention relates to a semiconductor composite apparatus, an LED that employs the semiconductor composite apparatus, an LED printhead that employs the LED, and an image forming apparatus that incorporates the LED printhead.
2. Description of Related Art
FIG. 33 is a perspective view illustrating a pertinent portion of a conventional LED printhead 500. FIG. 34 is a fragmentary top view of an LED array chip 502. This LED array chip is used in the LED printhead 500 in FIG. 33. The LED array chips 502 and driving IC chips 504 are mounted on a substrate 501. Bonding wires 506 connect between electrode pads 503 of the LED array chips 502 and corresponding electrode pads 505 of the driving IC chips 504.
With the LED printhead 500 in FIGS. 33 and 34, the electrode pads 503 and 505 are used for wire bonding, and have to be relatively large in area, e.g., 100×100 μm. For this reason, the surface areas of the LED array chip 502 and driving IC chip 504 are large. This makes it difficult to reduce the manufacturing cost of the LED array chip 502 and driving IC chip 504.
The LED array chip 502 has a light emitting region 507 having a depth of about 5 μm. There is the possibility that the wires contact the end portions of the IC chips and LED array chips. For reliable bonding, the LED array chip 502 should have substantially the same thickness as the driving IC chip 504 (e.g., 250-300 μm). Wire bonding exerts a large impact on the chips and therefore the thickness of the LED chip cannot be thin. This is another reason why the material cost of the LED array chip 502 cannot be reduced.
Japanese patent (Kokai) No. 10-063807 discloses a technique in which the pads on the light emitting elements may be connected to the pads on the substrate by flip-chip bonding instead of wire bonding. However, flip-chip bonding also requires bonding pads on the light emitting element (i.e., bonding pads having a certain size are required). Thus, use of flip-chip bonding that uses a paste is limited in reduction of material cost.
Another method is to bond a semiconductor such as a thin film light emitting element directly onto a substrate. This method eliminates pads that require a large area. When a semiconductor thin film device is bonded directly onto a substrate without using a paste, the adhesion of the semiconductor thin film to the substrate highly depends on the flatness of the bonding surfaces.